I think the downvotes fall into two categories. Some people agree with the renaming, and others just don't care either way. In a subthread about why people might want to move away from SF, "they're going to rename some schools" is not particularly relevant, and comes off a little flamebaity.
My personal opinion is that some of the renaming is a bit over the top, but I'm glad we're re-examining our historical "heroes"; most of what kids read in their US history classes paints an idealized, unrealistic picture of these figures, and ignores real harm they caused, both by their actions and attitudes. Regardless, I just frankly do not care whether a building is named Lincoln High School or John Doe High School. If ditching Lincoln's name makes a bunch of people feel more comfortable, it's no skin off my back.
What's actually important is that we teach the truth, and all of it. When we teach kids about Thomas Jefferson, we should certainly give him credit for the statesman he was, and for what he did to free the US from England. But we should also teach how he owned slaves throughout his entire life and saw no problem with that, and how he was a rich, elite landowner who believed that only a very small, single-digit percent of the population should be allowed to vote. Even Washington, who seemed not entirely comfortable with slavery, owned a slave that was only set free upon Washington's death. And Lincoln... well, his main concern was keeping the Union together. If that ultimately meant allowing the South to keep slavery intact, he was fine with that.
I don't bring all that up to say that they were awful, irredeemable people with no positive qualities. Some of them, if born today, might grow up with very different attitudes. But I think it's reasonable to suggest that quite a few people, especially non-white people, might not be particularly comfortable sending their kids to schools named after these people. And it's perfectly ok that they feel that way.